Photographic treating solutions containing ferricyanide ions and alpha ether carboxylic acid compounds



I'PHOTOGRAPHIC TREATING SOLUTIONS .eoN-

TAINING FERRICY ANIDEJONS -ALPHA ETHER CARBOXYLIC ACID COR/ POUNDS Jacob Quentin iUmberger," HolmdeL' N..;l.,:aassignor sto E. .1. 'di! lout de NemoursandCompany,Wilmington, 'Del.,-'a corp'oration: o'f Delaware "No Drawing. ApplicatiomApril 15,1953,

Serial No. 349,089

This invention relates to inorganic 'toningcompositions. More particularly it relates to-mor-ganlc toning baths and to processes .of-intensif-ying photographic imagesnwith .such baths.

"Various toning baths are known in .the photographic art.

widespread use. They generally include ionic. and ferricyanide ionsand a-sequesteringand buffering agent. The latter agent is.usually citric ia'cid -or oXal1c,--ac1d.

These conventional iron toners -.-are .-son1ewhat.-unstable due in part to theoxidation'of the citric or' oxalicaacid .eompound by :ferric vand/or ferricyamde '10I1S. They .have=the further shortcoming of --being very.-corros1ve.1to

metal surfaces. This :is due primarily .to the low,pH .(about 1\to'2-) of-the-solution. -When.alkalies are-added .to raise the pH it has been -found .that the-degree 10f intensification is reduced. '.Similarly, if chromates-are .addedto-reduce corrosion, the .degree of intensification :is (reduced. fIhis reduced intens1ficat1on is due to OK!- dation of the silver image by the anti-.corrosion-agent. An object of this. invention :is to ;provide {improved photographic toning baths. Another. objectisto provide photographic iron toning baths :which are free ;from the above disadvantages. A- more .specifio object is to 11-Provide iron-toning baths which havezreduced corrosive properties and increasedstability. Still ifurther objects will be-apparent from the following. description of the invention.

The above objects are accomplished 'by%the.toning=solu- .tions of this invention which comprise an aqueous-solution containing ferricyanide ions,.;cationszthataform relatively insoluble ferrocyanlde "compounds and. an alpha ether carboxylic acid compound of :the formula:

=wherein M is hydrogen or other water-soluble, saltforming .cation, e. g., ilithium, sodium;:potassium;eammonium, substituted.. ammonium,e. g, tetramethylcand stetraethylammonium ..or ..an amine, and ..:R; is azmono- QO-GHHC OH I p-nitrophenoxyaceticacid,

2,7-naphthoxydiacetic acid,

States Patent 'ice starch glycolic acid, starch ('0CH2'CO0H)11I and cellulose glycolic'acid "or "carboxymethyl cellulose, cellulose (--OCH2COOH)n, where *nis'a positive integer, aagd 'theirzrsaltswith :the:.salf-.forming cations mentioned at ,ove.

The amount of the alpha-ether carboxylate compfound present in the bath used for toning silver images will, of course, depend on the particular compound in questionand to a lesser extent on the particular film to' be =treatedand=fother-constituents 'of theI bath. "Concentrated stock solutions are comprehended by -"the inventionand they can be-diluted prior to-use. The 's'olutions can' be made by simply adding the various constituents-to water in any order except in cases where"the ingredients-are added. in a certain .order to prevent precipitates, such vas ferric hydroxide, from .forming.

Of :these, iron-toning baths have enjoyed .rather toning silveriimageswith the toning The invention willbeiurther'illustrated but isnotlim- -.ited .bythe yfollowing examples.

":EXAMPLE I The following toning bath is madeby adding the con- .stituents in the order named with stirring and after vwaitingjtor the previous constituent to be completely .Jdissolved: Y

Water Diglycolic 'acid ;gms 3050 Sodium hydroxide gms 18:0 Ferric nitrate-9H2O gms 1420 Potassiumbromide ....'gms 2.0 Potassium ferricyani'de gms "5. 0

-'Water:to make 1.0 liter.

'T lThis bath has a pH approximately 4.5. at 77 F. ,A...silver rimagejn a photographiefilm can be adequately .toned 'in-this. bathin .sevennu'nutesat 77 F. Thetpotassium bromide can be relirninated .withsimilar.results.

:fiXAMBLE-II .The .following toning bath .is.made after the manner Water to'make 1.0 liter.

- This; bath .has" a pH of approximately 5 .and is especially :.useful for. blue toning Roentgenograms or radiographs. Twhe=molybdicacid further reduces corrosion -of metal surfaces 1 without-impairing the formationof ;the :blue pigment. Similar/useful "toning baths" can be madeby .-.substit-u.tin galkali metal salts of molybdic .acid ortun-gstic itacideor .the .latter acid .tor the molybdic (acid of -.this

-.example.

Similar -.results are-obtained :by.-adding 30 grams of potassium thiocyanate to the solution of Example zI'I. .It-actsas a-fixing agent for-silver salts which-otherwise wou-ldzmart-h'e clarity of the Roentgenogrameby light- :scattering-action.

* The following examples illustrate furtherprocesses -of baths-of this inven t-ion.

EXAMPLE III FFhe front and rear film elements of the type described :in Jennings 'U. "S.' Patent 2,462,503,'jExample, l,. .except that the yellow filter dye of ExamplefZ of2Gaspar.U.I S. 2,274,782 Was used instead of colloidal .silverjn the ;blue record emulsion, and the coating Weights oft-silver thalide were different, the blue record.:being 35 .mg...per square dec., green record mgaper :square .dec.,'.'and red record 87 mg. per square dee., were exposed while *in emulsion-toemulsion contact ;to.a :multicolor scene. :Also boric'facid :was added tothetwo photosensitive :emulsions offthe front film .lIO prevent premature "stripping of the film during processing.

The r'e'd-recordinegative wasdeveloped "nine minutes at 68 F. -:to gamma 0.8 in developer prepared as follows:

Water -..ml.. F7501) Mono-methyl para-aminophenol HzSO4 gms 1 Hydroquinone gms 2.0 Sodium sulfite, anhydrous gms 50.0 Borax gms 7.5 Potassium bromide gms 02 Water to make 1.0 liter.

The front film was developed in the same developer (pH approximately 8.8) for 14 minutes at 68 F., fixed 1n a hardening fixer mixed as follows:

Water to make 1.0 liter, Acetic acid, 28% to make pH 4.0,

for 14 minutes at 68 F., washed 14 minutes and dried.

The rear film (red record) and the processed front film (green record-the low gamma blue record component being insignificant) were printed into the cyan and magenta color forming layers, respectively, of a multilayer color print film of the type described in the Jour. Motion Picture and Television Eng, November 1950, pp. 455-476. Then the processed front film was placed in a 2% aqueous solution of oxalic acid, which treatment permitted the easy removal of the outer, green record emulsion layer. The blue record emulsion layer remaining on the front film support was then toned by seven minutes treatment in the blue toning bath of Example I at 68 F., washed and dried.

The intensified blue record image was then exposed into the yellow color-forming layer of the aforementioned color print film, which was then processed to a color reproduction as described in the above reference. Good color rendition was obtained since the iron toner increased the gamma of the blue record image from 0.2 to 0.8 to the green printing light used to expose the yellow color-forming layer of said color print film.

EXAMPLE IV A perforated photographic motion picture stripping film of the structure described in Jennings U. S. Patent 2,462,503 (column 6, lines 64 to 66) in which a gelatinosilver bromoiodide photosensitive emulsion was used to produce a silver halide coating weight of 35 mg. per square dec. for the green-blind red-sensitive layer which contained 1,l'-diethyl-2,4-carbocyanine iodide and boric acid, said layer being nearest the film support, and a silver halide coating weight of 75 mg. per square dec. was used for the outer orthochromatic gelatin-silver halide emulsion layer which contained 1,1'-diethyl-2,2'-cyanine iodide as the green-light sensitizing dye and the dye of Example 2 of Gaspar U. S. Patent 2,274,782 as a yellow filter dye and boric acid, which layer was coated on an intermediate sodium-o-sulfobenzaldehyde polyvinyl acetal stripping layer, was placed in a camera in emulsion-to-emulsion contact with a blue-record front film as disclosed in said Patent 2,462,503 and exposed to a multicolor scene, the entrant light first passing through a blue-record front film. The front film comprised a cellulose acetate film base which was coated with a gelatino silver bromoiodide emulsion to a coating weight of 17 mg. silver halide and 75 mg. gelatin per square dec. The films were removed from the camera and the front film was developed for about five minutes at 68 F. to gamma 0.18 with normal agitation in a negative developer made by admixing the following components:

Water cc 975 0 Mono-methyl para-aminophenol-HzSO4- gms 0.8 Sodium sulfite, anhydrous gms 90.0 Hydroquinone gms 1.0 Borax gms 3 0 Potassium bromide gms 01 Water to make 1.0 liter.

This solution had pH 8.9 at 68 F. Following fixing, washing, and drying, the low gamma silver image was intensified by 7 minutes treatment in the toning solution of Example I.

The rear multilayer film was processed as follows: (a) developed for 14 minutes at 68 F. with normal agitation in the foregoing developer whereby the outer layer was developed to gamma 0.8 and the inner to gamma 0.31,

(b) fixed for a. period of 14 minutes in a hardening fixer made by admixing the following components:

Water cc. 500.0 Hypo gms 300.0 Sodium sulfite, anhydrous gms 11.0 Acetic acid, 28% cc 45.0 Potassium alum gms 10.0

Water to make 1.0 liter,

(0) the fixed film was washed for a period of five minutes in cold running Water and dried. The outer emulsion layer exhibited good adherence to the inner layer due in part to the inclusion of boric acid in the emulsions prior to coating. Then the rear film was soaked for 30 seconds in the following emulsion-transfer solution at 78 F.:

Water to make 1.0 liter,

and the wet outer emulsion layer was then pressed into intimate contact with a second similarly perforated gelatin blank film comprising a transparent cellulose acetate film base coated with a gelatin layer to a weight of about mg. per square dec. The outer layer was then stripped from the remaining red-record, and the blank film with its adherent image record was washed and dried. The red-record negative silver image remaining on the original rear film base was intensified to gamma 0.8 by first bleaching it in an aqueous potassium ferricyanide solution containing potassium bromide and then developing it to such a gamma in a color developing solution containing N-diethyl p-aminoaniline hydrochloride, a phenol, sodium carbonate, potassium bromide and a small amount of sodium sulfite. A cyan colored dye image was formed in situ with the developed silver image. The gamma was 0.8 to the red light used to print this color component negative into the print film below.

The three separate film elements containing the colorseparation silver image records were then separately printed into the appropriate layers of a multilayer color print film of the type described in the Journal Motion Picture and Television Engineers, November 1950, pages 455-476. This multilayer film was composed of a cellulose acetate base having a removable antihalation backing on one side and yellow, cyan and magenta colorforming polyvinyl acetal polymer-silver halide emulsion layers coated in that order on the other side of the base. A yellow filter material (e. g., Tartrazine C. I. No. 640) was present in the magenta color former emulsion layer. The exposed multilayer color film was then color-developed at 68 F. in a solution made by admixing the following components:

I Grams N-diethyl p-aminoaniline hydrochloride 2.5 Sodium sulfite, anhydrous 10. Potassium bromide 2.0 Sodium carbonate, monohydrate 47.0

Water to make 1.0 liter,

for ten minutes and processed to a color print as described on pp. 469-471 of the above reference.

EXAMPLE V 1 A high-speed X-ray film bearing a gelatino silver bromoiodide (96:4 molar ratio) emulsion layer having a coating weight of 103 mg. of silver halide per square dec. coated on each side of a waterproofed cellulose acetate film base 0.008 inch thick was intercalated between intensifying screens and exposed to a human head for second by X-rays from a conventional medical X-ray apparatus. The exposed Roentgenogram was then developed for five minutes at 68 F. in a fastacting metol-hydroquinone developer, rinsed ten seconds in water, fixed ten minutes at 68 F. in a conventional hardening fixer, washed 20 minutes and dried.

This Roentgenogram appeared greatly under-exposed when compared with a normal exposure of second. However, when the under-exposed film was toned for five minutes in the following solution at 68 F., the exposure appeared normal. When viewed through a red filter which transmit substantially all of the visible wavelengths greater than 600 millirnicrons (such as the Wratten No. 25 filter), the contrast of the image was greatly enhanced and tissue relatively non-opaque to aeaaaaa Xvrays, such as.the. human.eaig waselearlyv discernible... Through a bluefilter the..contrast.was.lower. and .p er+ nnttediobservation of the, relatively. opaquebone. tissue.

Toning bath.

Water ml 500.0 Di'glycolic acid gms- 60.0 Sodium hydroxide grns 3610 Eerric nitrate-9H'2O gms 14.0 Molybdic acid, 85% M00; gms 1.0 Potassium ferricyanide gms 5.0; Potassium' bromide gms 2.0

Water. to. make 1.0 liter.

This solution had pH 4.95 at 68 F.

EXAMPLE .VI

The front film oftExampl'e; IV. was-exposed, developed:

forrten minutes. at..7.0. E., fixed, washed, and dried; as.

in: said: example exceptthat the: following; colorcou.- pling developer was substituted for the: conventional blackrand-fwhite developer:

Water-to make. 1.0 liter:

TZhe-pHwas-adjusted, to; 11.5 withv 1. molar NaOH (ap proximately; 6.51 .ml-.)-. The filnmcontaining the. magenta dyeiimage was. then tonedfor approximately seven minutesat 25 C. .in an -iron toner mixedas follows:

Water ml 700.0 Ferric nitrate-9Hz0 gms- 3.5' Diglycolic acid ..gms 16.0 Potassium bromide; gms 6.0 Potassiumferricyanide gms 1.0

Waterto make. 1.0-liter;

Sufiicient 3-molar NaOHwas thenadded. to make. pH 4.02 at. 25 C. Following washing andidrying, the difl fuse opticaldensity Of.'1h6 film vstrip was :determined to green lightof. dominant. Wavelength about: 5.50 milli-. microns. area. of optical. density 0.35 due/to. ele+ mentary silver wasdncreased'to over3.0 bythedeposh tionof magenta-dye andtironblue. pigment.

EXAMPLE VII Water: 400.0 ml. A1pha-ether carboxylic acid; 0.224 to 448-: moles. 10 molar. sodium hydroxide solution to: make=pH 5.15 at C. Ferric nitrate-91420" (in 50 ml.

H2O) 14.0 igms. Potassium ferricyanide (in 50ml.

H2O) .5.0gms.

Water to make 0.95 liter.

AdjllStr'tO pH; 4.6. at'25 C. using 10% nitric acid or 10% aqueous borax..

Water to .make, 1.0i1iter;

When precipitationuoccurred upon adding the: ferric nitrate, the OLrfifl'lCI' carboxylicv acid was added.in-the higher. concentration. indicated. Each. of the toning baths produced characteristic blue-toned images; In the v..case...of.zethylene .bis .glycolic ,acidthe blue ,image was slightly. more transparent than when the. diglycolic. acid toner was used. The toning bath containing..meth'oxy.- acetic. acid produced a blue. image of exceptional. clarity and transparency especially in areas of i high density.

EXAMPLE. VIII 1 A Roentgenogram was: exposed and processed as in:

Example V and; iron-toned in a-v solution prepared'asa follows:

Grams; Potassium ferricyanide 1.02 Ferric nitrate-9H2O 3:5':

Diglycolic. acid 50.0 Sodium chloride 6.0.

Sodium. hydroxide. 27 .6;

Water. to make. 1.0.1iter:

pH=4;4 at 77 F:

The solution intensified.- some ofi the silver. fogof'the. Roentgenogram. When sodium hydroxide was. added to raise the pH'to.4;8, fog intensifi'cation was-greatly'de creased. Similarly, on addition of 1. to. 2. grams of: KF- 2H20 (potassium fluoride hydrate), the fog intensi fi'cation was decreased; Addition of more, diglycolic' acid and sodium hydroxide similarly decreased fog inttensification.

EXAMPLE; IX-

An under-exposed Roentgenogram made fromla film; of thetype; described. in Example V was: treated. for. a. period. of. eight minutes. at room temperature. in. the. following toning bath which had. pH.5.-0:0.1 at room. temperature:

Water, .to make 1.09 liter;

he sodium .nitrite of- Example X: decreasedcorrosioni more strongly than did; the; molybdicjacid :in: other examples. Other water-soluble: nitrites, e. g;, potassiumnitrite, lithium nitrite andammonium nitrite can-be used.- inlike manner. Thetorange: dye stained thfi'fillllglfi duced the overall blueness of the image, andfimprovedthevisual contrast of the-image:

The. alpha-ether carboxylic acid compounds-which are described above are not'ilimited in their use to the specific toning solutions or baths described, above. but: can-be usedin any inorganic toner containingg ferricy anideion'as theoxidizing agent. The baths; for example, may-contain lead,- nickel,.mereury,.copper,. tin, uranyl; vanadyl, etc., ionsin.- addition to; the; ferricyanide ion.-

In place. ofsthe ferricsnitrateof the:toners.- intthe.-extamples one can substitute. other equivalent inorganiciron. compounds, e. g,, ferric. chloride; ferric" bromide-,uferric. fluoride, ferric sulfate, .etc. Mixtures of.two or more-of. the ferric salts can besused.

The-invention, moreover,- isnot. limited.- to potassium ferricyanide as-the ferricyanide .salt. Suitable additional. salts include lithium, sodiumand ammoniumferricyanide. Mixltures of two or more soluble ferricyanides canebet use Various bases-oralkalies other than: sodium hydroxide: can be used. to raise or adjusttth'e pH-of the toning;.-solutions. Among vsuch compounds are potassium hydroxide, sodiumtbicarbonate, borax sodiurn-lacetateg amines,- e. g, dimethyl'arniue, diethyl amine,- n-propyl, n=butyland npentyl amine, cyclohexyl' amine;. piperidine, etc. The amount by Weight of such bases-or alkaliesinthe: toning baths can be greater. than prior-art.toningbathsuwithout impairing the: intensification-of; the silver image. Thus, sufficient alkaline compoundto raise-the pH to -4 too-may; beused with: good results becauseroflthepresenceof the. compound of formula R(OCH2COOM)n-..

The relatively high pH iron-toners of. this inventiorr constitute media of relatively low-oxidation or electron, acceptingv potential. Hence, it is 'possibleto add silver. halide solvents such as; thiocyanatesalts to'these: iron: toners. This results in a combination fixer and iron-toner or usable stability.

Diglycolate ions inaqueousiron-toner solutions. man"- age to prevent precipitation of insoluble iron-salts butstillpermit the: formation of-;blue pigment'infilms-containing, a silver image. In the preferred pHrange-ofthezirom toners, i; e., pH: 3 to 6; sequestering agents suchas-citrates and ethylene diamine tetraacetate apparently sequester the ferric ions so well as to appreciably weaken the blue pigment density intoned films. The latter sequestering agents as well as others. e. g., potassium fluoride, nitrilo triacetic acid and methylamino diacetic acid, can be used in combination with diglycolate ions or any of the compounds of Example VII.

The invention is particularly useful in increasing the speed and contrast of Roentgenograms and radiographs. For example, the contrast of iron-toned images may be conveniently varied by use of differently colored filters for viewing as in X-ray use or photographic printing in general. When viewed through a red filter, the contrast of irontoned Roentgenograms is very high-permitting the diagnosis of tissue normally not clearly outlined due to low opacity to X-radiation. Through a blue filter the contrast is low but the latitude is high. Thus, by use of appropriate filters one can diagnose tissue both of low opacity to X- radiation (yellow, orange or red filter) and of high opacity to X-radiation (blue or no filter).

In some of the existing X-ray film products a blue tint is incorporated in the film to improve its viewing characteristics. The necessity for such tinting is removed if the iron-toner is adjusted so as to produce overall blue tint through intensification of fog. Gelatin hardeners, such as potassium alum, are advantageously added to the toning solutions of this invention.

The invention also is useful in increasing the intensification of under-exposed or under-developed negatives or positives where a blue-toned image is desired. Blue-toned negatives can be made to exhibit variable contrast to a panchromatic print medium depending on the spectral quality of the light transmitted by the printing filter.

The toning baths of the invention can be used to increase contrast to red light by as much as times. This makes them useful in preparing travelling silhouette mattes or masks for combining foreground and background scenes of different origin. In the Williams process for silhouette formation, unlighted black velvet is used as a backdrop and usually appears lighter in the negative than any part of the illuminated foreground. A high contrast print can be made and by repeated operations the contrast built up until the background is clear and the foreground completely black or vice versa. This silhouette constitutes the travelling matte. For example, one can take a black and white motion picture negative film, expose it, develop it to gamma 0.75 in a conventional metolhydroquinone cine negative developer, and then iron-tone it with the toning bath of Example I for seven minutes at 68 F. When read on an electronic photometer (densitometer) employing electromagnetic radiation of Wavelength 700 millimicrons, two exposure regions which differ by only 0.03 in silver density can be intensified to a density dilference of 0.50. This helps one to distinguish between the unlighted black velvet background and any dark object in the foreground and thus facilitates the preparation of a silhouette especially when red light is used to print the iron-toned negative into a red-sensitive, high contrast film or other printing medium.

The high degree of intensification obtainable by the iron-toning baths and processes of this invention makes possible the use of very low silver halide coating weights in the front film of bipacks or tripacks or in the blue record emulsion layer of stripping films. This is conducive to high speed and resolution in the layers behind or beneath the front film or blue record emulsion, respectively.

The invention obviously is not limited to the toning of the stripping films described in Jennings U. S. Patent 2,462,503 which have stripping layers composed of watersoluble acetals of vinyl alcohol polymers. To the contrary, the stripping layers may be composed of other polymeric materials including the polymeric aminonitrogen containing materials described in Marasco U. S. Patent 2,182,814, Jour. Society Motion Picture and Television Engineers, April 1950, pp. 445-446, and the polyvinylpyridine quaternary salts described in Richards U. S. Patent 2,487,829 and Umberger U. S. application Ser. No. 115,943, filed September 15, 1949, now Patent No. 2,612,446.

An advantage of the invention resides in the fact that the compounds of the formula R(OCH2COOM)n are resistant to oxidation (viz., loss of electrons) and enable one to prepare toning baths of high degree of intensification at pH range 4 to 6.

Diglycolic acid, the preferred acid, falling within Formula I, has the advantage that it is cheap, non-volatile,-

and highly soluble in Water. It sequesters Fe+++, but not so strongly as to prevent formation of blue pigment by the action of an iron toner on a silver image. At pH approximately 4.5 the acid exists half as the doubly-charged anion and half as the singly-charged anion. Thus, diglycolic acid is a good buffer in the pH range 3 to 6, the preferred pH range for our improved iron toners.

A still further advantage of the invention is that with these comparatively high pH iron toners it is possible to blue tone a color-coupler developed silver image without destroying or removing the color-coupled dye image in the film. The acid iron toners of the prior art destroy such dye images.

By raising the pH and the sequestering agent concentration, one is able to control and reduce the intensification of development fog. This is very useful for X-ray film intensification. Also, in the case of treating a beaded sound track, one can use the iron-toning baths in which the fog is reduced to a low level.

As many widely different embodiments of this invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be limited except as defined by the claims.

What is claimed is:

l. A composition comprising an aqueous solution containing fer-ri-cyanide ions, cations that form relatively insoluble ferrocyanide compounds and an alpha ether of a carboxylic acid compound containing at least one radical of the formula OCH2COOM, wherein M is a member taken from the group consisting of hydrogen and water-soluble salt-forming cations, taken from the group consisting of diglycolic acid, methoxyacetic acid, o-methoxyphenoxyacetic acid, p-nitrophenoxyacetic acid, 2,7- naphthoxydiacetic acid, ethylene bisglycolic acid, starch glycolic acid and cellulose glycolic acid and their water- -soluble salts.

2. A composition comprising an aqueous solution containing ferricyanide ions, cations that form relatively insoluble ferrocyanide compounds and an alpha ether of a carboxylic acid compound containing at least one radical of the formula OCH2.COOM, wherein M is a member taken from the group consisting of hydrogen and water-soluble salt-forming cations, taken from the group consisting of diglycolic acid, methoxyacetic acid, o-methoxyphenoxyacetic acid, p-nitrophenoxyacet-ic acid, 2,7-naphthoxydiacetic acid, ethylene bisglycolic acid, starch glycolic acid and cellulose glycolic acid and their water-soluble salts, a water-soluble nitrite and a watersoluble thiocyanate.

3. A composition comprising an aqueous solution containing ferricyanide ions, cations that forms relatively insoluble ferrocyanide compounds and diglycolic acid.

4. A composition comprising an aqueous solution containing ferric nitrate, sodium hydroxide, potassium ferricyanide and diglycolic acid.

5. A composition comprising an aqueous solution containing ferric nitrate, sodium hydroxide, potassium ferricyan-ide, molybdic acid and diglycolic acid.

An aqueous photographic toning solution containing ferricyanide ions, cations that form relatively insoluble ferrocyanide compounds and diglycolic acid anions in an amount of 10 to 200 grams per liter of solution.

. 7. The process which comprises treating a photographic element containing a silver image in an aqueous solution containing ferricyanide ions, cations that form relatively insoluble ferrocyanide compounds and an alpha ether of a carboxylic acid compound containing at least one radical of the formula -OCH2COOM, wherein M is a member taken from the group consisting of hydrogen and water-soluble salt-forming cations, taken from the group consisting of diglycolic acid, methoxyacetic acid, o-methoxyphenoxyacet-ic acid, p-nitrophenoxyacetic acid, 2,7- naphthoxydiacet-ic acid, ethylene bisglycolic acid, starch glycolic acid and cellulose glycolic acid and their watersoluble salts.

8. A process as set forth in claim 7 wherein a dye of a color which is approximately complementary to that of said insoluble ferrocyanide compound is present in said solution.

9. The process which comprises treating a photographic element contain-ing a silver image in an aqueous solution containing fer-ricyanide ions, cations that form relatively insoluble ferrocyanide compounds and diglycolic acid.

10. The process which comprises treating a photographic element containing a silver image in an aqueous solution containing ferric nitrate, sodium hydroxide, posolution containing ferric nitrate, an alkali, potassium tassium ferricyanide, sodium nitrite and diglycohc acid. ferricyanide and diglycolic acid.

111; The process which csnlilprises treating a photo- 6 References Cited in the file of this patent grap ic e ement containing a s' ver image in an aqueous solution containing ferric nitrate, sodium hydroxide, po- UNITED STATES PATENTS tassium ferricyanide and diglycolic acid. 2,625,475 Russell et a1 I an. 13, 1953 12. The process which comprises treating a photo- 2,625,476 Henn Ian. 13, 1953 graphic element containing a silver image in an aqueous 

1. A COMPOSITION COMPRISING AN AQUEOUS SOLUTION CONTAINING FERRICYANIDE IONS, CATIONS THAT FORM RELATIVELY INSOLUBLE FERROCYANIDE COMPOUNDS AND AN ALPHA ETHER OF A CARBOXYLIC ACID COMPOUND CONTAINING AT LEAST ONE RADICAL OF THE FORMULA -O-CH2COOM, WHEREIN M IS A MEMBER TAKEN FROM THE GROUP CONSISTING OF HYDROGEN AND WATER-SOLUBLE SALT-FORMING CATIONS, TAKEN FROM THE GROUP CONSISTING OF DIGLYCOLIC ACID, METHOXYAVETIC ACID, O-METHOXYPHENOXYACETIC ACID, P-NITROPHENOXYACETIC ACID, 2,7NAPHTHOXYDIACETIC ACID, ETHYLENE BISGLYCOLIC ACID, STARCH GLYCOLIC ACID AND CELLULOSE GLYCOLIC ACID AND THEIR WATERSOLUBLE SALTS. 